Abstract
Noble metal nanoparticles or subnanometric particles confined in zeolites, that is, metal@zeolite, represent an important type of functional materials with typical core–shell structure. This type of material is known for decades and recently became a research hotspot due to their emerging applications in various fields. Remarkable achievements are made dealing with the synthesis, characterization, and applications of noble metal particles confined in zeolites. Here, the most representative research progress in metal@zeolites is briefly reviewed, aiming to boost further research on this topic. For the synthesis of metal@zeolites, various strategies, such as direct synthesis from inorganic or ligand‐assisted noble metal precursors, multistep postsynthesis encapsulation and ion‐exchange followed by reduction, are introduced and compared. For the characterization of metal@zeolites, several most useful techniques, such as electron microscopy, X‐ray based spectroscopy, infrared and fluorescence emission spectroscopy, are recommended to check the successful confinement of noble metal particles in zeolite matrix and their unique physiochemical properties. For the applications of metal@zeolites, catalysis and optics are involved with an emphasis on catalytic applications including the size‐dependent catalytic properties, the sintering‐resistance properties, the substrate shape‐selective catalysis, and catalysis modulation by zeolite microenvironment.
Highlights
applications in some key industrial processes.[1,2,3,4,5,6,7] Generally, the metal partithat is, metal@zeolite, represent an important type of functional materials cles, according to their sizes, can be distinwith typical core–shell structure
The particle size is known as a vital metal@zeolites, various strategies, such as direct synthesis from inorganic or ligand-assisted noble metal precursors, multistep postsynthesis encapsulation and ion-exchange followed by reduction, are introduced and compared
We will focus on the important catalytic applications of noble metal particles confined in zeolites, and some other emerging applications in optics will be included
Summary
Zeolites are usually synthesized by a process of slow crystallization of a silica-alumina gel in alkaline or fluoride media at elevated temperatures. A hydrothermal synthesis after a sol-gel processing. Changing the synthesis conditions, such as the pH values of the gel, crystallization temperatures, and types of organic structure directing agents (OSDAs), might show significant impacts on the crystallization process and direct toward zeolites with different framework topologies.[30,31] On the other hand, the preparation of noble metal particles requires the strict control of experimental conditions since the high pH values and/or temperature will generally lead to the aggregation of particles.[32,33] it is quite necessary to explore the feasible combination between the synthesis of zeolite crystals and the regulation of noble metal particles, especially in the case of direct synthesis strategy
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